The objectives of the proposed research are to provide a description of several interrelated neural and photochemical events subserving visual adaptation in the vertebrate retina: (a) to examine the role of the various retinal elements in the adaptation process, (b) to elucidate the mechanisms by which information is transferred between neurons, and (c) to identify the chemical agents which are responsible for transmission at chemical synapses. Emphasis will be placed on studying the effects of light-and dark-adaptation on photopigment kinetics, the concomitant changes in the elctro-retinal potentials, and the activities of substances which may act as transmitter agents in the distal retina. Intracellular recordings from photoreceptors and horizontal cells will serve to monitor the effects of various putative transmitters, their analogues, and blocking agents on the membrane potentials and light-evoked activities of these cells.